1. Field of the Invention
The invention relates to a doped semiconductor wafer of float zone-pulled semiconductor material and to a process for producing the semiconductor wafer. The process comprises the production of a doped single crystal by float zone pulling (floating zone crystal growth, FZ method) and the division of the single crystal into semiconductor wafers. During the pulling of the single crystal, a molten material which has been produced using an induction coil is exposed to at least one rotating magnetic field and is solidified. The single crystal which is formed during the solidification of the molten material is rotated.
2. The Prior Art
The use of a rotating magnetic field in float zone pulling is described, for example, in DD-263 310 A1. However, the process which is proposed in this document attempts to make the diffusion boundary layer thickness more uniform. However the present invention achieves the most homogeneous distribution of dopants added to the molten material possible and of reducing striations. A homogeneous dopant distribution manifests itself in a tight radial macroscopic resistance distribution.
Striations are macroscopic dopant fluctuations. They are usually quantified by carrying out a spreading resistance analysis on the semiconductor wafer.
The radial macroscopic resistance distribution is measured by the four-point methods described in ASTM F 84, taking a mean over a length of several millimeters.
Hitherto, it has been attempted to homogenize the dopant distribution and therefore reduce the radial resistance variation by varying the crystal rotation, by displacing the induction coil relative to the crystal axis and by changing the shape of the induction coil. A drawback of these measures is that they often lead to an increase in the dislocation rate and to a reduction in the process stability.
It is also known that very flat radial dopant profiles can be set by neutron doping. However, neutron doping has a large number of drawbacks. For example, the method is only suitable for semiconductor material with a resistance of approximately 3 to approximately 800 Ohm*cm. Radiation damage which has to be annealed by a thermal aftertreatment is inevitably produced. Nevertheless, it is impossible to prevent a reduction in the minority charge carrier life. Furthermore, necessary decay times, the thermal aftertreatment and associated conveying operations make the method time-consuming and expensive.